Method of forming a protective inner liner on a metal container



United States Patent METHOD OF FORMING A PROTECTIVE INNER LINER ON AMETAL CONTAINER Anthony S. Scheibelhoffer and Richard K. Lewis, CuyahogaFalls, Ohio, assignors to The Goodyear Tire & Rubber Company, Akron,Ohio, a corporation of Ohio No Drawing. Continuation of application Ser.No.

456,504, May 17, 1965. This application Nov. 13,

1967, Ser. No. 682,666

6 Claims. (Cl. 117-96) ABSTRACT OF THE DISCLOSURE A method of forming aprotective seamless inner liner on the interior surface of a metalstorage container which comprises applying at least one spray coat of anonfiammable liquid polyurethane reaction mixture to the interiorsurface of the said container and curing the spray coats of polyurethanemixture to form the inner liner.

This application is a continuation of Ser. No. 456,504, filed May 17,1965, now abandoned.

This invention relates to solutions of polyisocyanate modified reactivehydrogen-containing materials and to coated objects and other productsprepared therefrom.

Polyurethane rubber-like polymers have generally been applied aspolyurethane reaction mixtures prepared in highly flammable solventssuch as acetone, methyl ethyl ketone, benzene, and toluene which formexplosive mixtures with air in various proportions. Because of the fireand explosion hazards involved in the use of such solutions they werenot used in confined areas.

Storage tanks have been lined with rubber sheeting to cover weak or Wornareas and cracks and to increase their resistance to chemicals and,generally, to extend their useful life, increase their versatility andmake them easier to clean. Usually rubber linings are applied to theinterior of storage tanks as compounded calendered sheets of rubberwhich must be manually fitted, installed and heat cured. Considerableexpense is incurred in the labor required, and in special heatingapparatus. The cured rubber lining will normally have seams which aresubject to failure.

A liner for a chemical storage tank should be relatively stable to manychemicals over a wide temperature range. Such a liner should not have atendency to crack or rupture when subjected to jarring forces at varioustemperatures such as those experienced, for example, by a railroad tankcar. Rubber linings have not been completely satisfactory, and moresatisfactory linings have been sought. Polyurethane rubbers havesatisfactory properties for such linings but they have not beenextensively used because the application of such liners to closedvessels or tanks heretofore has been difficult and dangerous.

It is an object of this invention to provide nonflammable solutions ofpolyurethane reaction mixtures. It is a further object of this inventionto provide a nonflammable solution or mixture of each of the majorcomponents of the polyurethane reaction mixture. Another object is toprovide solutions of polyurethane reaction mixtures in non-flammablesolvents. A still further object of this invention is to provide amethod of forming a seamless protective integral liner in a metallicstorage container. It is another object to provide a method in which anon-flammable liquid polyurethane reaction mixture is applied to theinterior surface of the storage container, and cured to form a rubberyinert coating. Other objects will appear as the description of theinvention proceeds.

In accordance with this invention it has been found Patented Sept. 10,1968 that non-flammable solutions of polyurethane reaction mixtures andnon-flammable solutions of each of the major components of thepolyurethane reaction mixtures can be prepared in non-flammablechlorinated solvents. The non-flammable polyurethane reaction mixturesolutions can be used to coat surfaces of materials in confined areas toform a coating of a polyurethane polymer without incurring explosivehazardous conditions.

A non-flammable polyurethane reaction mixture solution according to thisinvention is a mixture which does not support combustion at atemperature of about 70 to about F. when exposed for 5 seconds to aflame having a temperature of from about 700 C. to about 800 C. andwhich is located one-half inch from the surface of the polyurethanesolution. The test is conducted with 20 to 25 cubic centimeters of thepolyurethane reaction mixture solution in a 40 to 50 cubic centimeterdish which has a diameter of from 2 to 2 /2 inches.

The polyurethane reaction mixtures of this invention as well as themajor components of the reaction mixtures can be prepared innon-flammable chlorinated solvents. Various non-flammable chlorinatedsolvents can be used. Representative examples of such solvents arechlorosubstituted olefins such as dichloroethylene, trichloroethylene,and 1,1,2,Z-tetraehloroethylene; and chlorosubstituted saturatedhydrocarbon compounds such as methyl chloroform, dichloromethane,1,.2-dichloroethane, trichloroethane, and 1,l,2,2-tetrachloroethane.Trichloroethylene is particularly useful.

The polyurethane polymers of this invention are usually prepared byreacting a reactive hydrogen-containing polymeric material with apolyisocyanate according to the following general procedure which isknown as the prepolymer method: The reactive hydrogen-containingpolymeric material is reacted with the organic polyisocyanate inproportions such that the ratio of isocyanate groups to the reactivehydrogen-containing groups of the reactive hydrogen-containing polymericmaterial is from about 1.1/1 to about 12/1 and preferably about 1.2/1 toabout 2.5/1. These materials are generally reacted at temperatures fromabout 20 C. to about C. The reactive hydrogens of the reactivehydrogen-containing polymeric material are supplied by hydroxyl groupsand amino groups. This prepolymer, itself a polyurethane, is thenusually dissolved or dispersed in the non-flammable sol vent to form asolution or dispersion which is then reacted with a catalyst, a chainextending agent, and/or a crosslinking agent to form a polyurethanereaction mixture.

Other methods known to those skilled in the art of preparingpolyurethane reaction mixtures with or without solvents being presentmay also be used.

The reactive hydrogen-containing polymeric material used in the reactionhas an average molecular Weight in the range of from about 700 to about5,000, generally in the range of from about 1000 to about 3500. Reactivehydrogen-containing polymeric materials useful in preparing thepolyurethanes of this invention are materials selected from the groupconsisting of polyester polyols, polyether polyols, polyhydroxylpolymers of conjugated diene hydrocarbons and castor oil.

The polyester polyols used in this invention are hydroxyl terminatedlinear polymeric polyesters derived from a glycol and an organicdicarboxylic acid. The polyester polyols are conveniently prepared byreacting a glycol with a dicarboxylic acid or its anhydride andcondensing the glycol ester formed to produce a polymeric polyester ofthe desired molecular weight. Ester interchange or other methodsfamiliar to those skilled in the art can be used if desired.

Representative examples of glycols which can be used for preparing thepolyester polyols are glycols such as ethylene glycol, the propyleneglycols, the butylene glycols, the pentylene glycols, hexamethyleneglycol and decamethylene glycol. Representative examples of organicdicarboxylic acids from which the polyesters can be derived arealiphatic dicarboxylic acids such as succinic acid, glutaric acid,adipic acid, suberic acid, sebacic acid, pimelic acid and azelaic acid;aromatic dicarboxylic acids such as phthalic acid, terephthalic acid andisophthalic acid.

Various polyether polyols are useful in this invention. Representativeexamples of such polyether polyols are polyalkylenearyl ether glycols,polytetramethylene ether glycols, and polyalkylene ether-thioetherglycols and triols. Generally the polytetramethylene ether glycols arethe preferred polyether polyols. Polyether glycols are particularlyuseful and can be prepared by polymerizing alkylene oxides such asethylene oxide, propylene oxide and butylene oxides alone or in mixtureswith each other or with another oxide. They can also be prepared byreacting one or more alkylene oxides with a diol such as ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol,hexamethylene glycol, and decamethylene glycol, a triol such ashexanetriol, higher alcohols such as pentaerythritol and the varioussugars, a polycarboxylic acid such as phthalic acid, with polybutyleneglycols, or with hydroxyl amines such as trimethanolamine.

Representative polyhydroxyl polymers of conjugated diene hydrocarbonsused in the invention are polyhydroxyl polymers of isoprene andbutadiene such as a 1,4 addition polymer of 1,3-butadiene having anaverage molecular weight of from about 1000 to about 4000 and anhydroxyl number of from about 112 to about 28, respectively.

Various organic polyisocyanate materials can be used in practicing thisinvention. Representative examples of such polyisocyanates are ethylenedisocyanate, propylene diisocyanate, tetramethylene diisocyanate,pentamethylene diisocyanate, octamethylene diisocyanate, undecamethylenediisocyanate, dodecamethylene diisocyanate and 3,3- diisocyanatedipropylether; cyclopentylene-1,3-diisocyanate,cyclohexylene-1,4-diisocyanate, toluene diisocyanate,xylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, 4,4-diphenyl propanediisocyanate, p-isocyanato benzyl isocyanate, m-phenylene diisocyanate,p-phenylene diisocyanate, furfurylidene diisocyanate, p,p',p"-triphenylmethane triisocyanate, methylene bis-4 phenyl isocyanate, ortho tolidinediisocyanate, and diphenyl-4,6-4'-triisocyanate. Generally, the aromaticdiisocyanates are preferred.

A catalyst can be used to facilitate the reaction which results in asubstantially reduced set-up time, and thus enhances the thioxotropicproperties of the polyurethane mixture. Well-known polyurethanecatalysts are useful for this purpose such as tertiary amines and thetin salts of fatty acids.

Agents which promote chain extension and crosslinking of the polymer arealso useful and are sometimes known as curing agents. Aromatic diamines,hydrocarbon diols such as ethylene glycol and propylene glycol,hydroxylamines such as triisopropanolamine, are used in this inventionas crosslinking agents. When crosslinking agents are used they areusually added to the prepolymer in a ratio of about 0.5/1 to about 1.5/1and, preferably, about 0.8/1 to about 1.0/1 amine and/ or hydroxylgroups of the chain extending and crosslinking agent for each isocyanategroup in excess of the reactive hydrogen groups of the reactivehydrogen-containing polymeric material.

Some aromatic diamines cause the reaction mixture to cure at arelatively slow rate while others cause curing to take placeconsiderably faster. Fast diamines are those diamines which develop aturbidity within about 30 seconds using the boiling methylene chloridetest. In this test half-molar solutions of the diisocyanate and diamineare each made up in methylene chloride. Equal amounts of the tworespective boiling methylene chloride solutions are mixed and the timerequired to develop a turbidity is measured. Those diamines which do notcause a tubidity to develop until after 30 seconds are considered to beslow diamines.

Representative examples of aromatic diamines which are slow curingdiamines are amines such as 4,4-methylene-bis, Z-chloroaniline, orthodichloro benzidine, and 4,4- bis amino phenyl sulfone. Representativeexamples of suitable fast curing diamines are 4,4-diamino-diphenylmethane, 3,3'-dimethyl-4,4 diamino diphenyl methane, 2,4-tolylenediamine, o-dianisidine, and o-tolidine.

The diamines can be dissolved in a flammable solvent, if desired, andthen added to the non-flammable chlorinated solvent. Various flammablesolvents can be used for this purpose such as ketones having boilingpoints below 165 C., for example, acetone and methyl ethyl ketone, oraromatic solvents such as benzene, toluene and chlorobenzene. Thesesolvents can also be added to a chlorinated solvent used to dissolve theamine. When such flammable solvents are used, they are used in amountssmall enough that the polyurethane reaction mixture solution remainsnon-flammable.

Other accelerators can also be used such as compounds having the generalformula HSA in which A stands for a thiazole, thiazoline, oxazole,imidazole, or imidazoline radical. The thiazole, oxazole and imidazoleradicals may be substituted with alkyl, aryl, and cycloalkyl radicals.The thiazoline and imidazoline radicals may be substituted with alkylradicals such as methyl, ethyl, propyl, and butyl radicals.Representative of these compounds are:

2-mercapto-4-methylthiazole Z-mercapto-4-methyloxazoleZ-mercapto-4-rnethylimidazole 2-mercapto-4-ethylthiazole2-mercapto-4-ethyloxazole 2-mercapto-4-ethylimidazoleZ-mercapto-4-n-propylthiazole 2-mercapto-4-n-propyloxazole2-mercapto-4-n-propylimidazole 2-rnercapto-4-n-butylthiazole2-mercapto-4-n-butyloxazole 2-mercapt0-4-n-butylimidazole2-mercapto-4,S-dimethylthiazole 2-mercapto-4, S-dimethyloxazole2-mercapto-4,S-dimethylimidazole 2-mercapto-4,S-diethylthiazole2-mercapto-4,S-diethyloxazole 2-mercapto-4,5-diethylimidazole2-mercapto-4,S-di-n-propylthiazole Z-mercapto-4,5-di-n-propyloxazole2-mercapto-4,5-di-n-propylimidazole 2-mercapto-4,S-di-n-butylthiazole2-mercapto-4,S-di-n-butyloxazole 2-mercapto-4,5-di-n-butylimidazole4-phenyl-2-mercaptothiazole 4-phenyl-2-mercaptooxazole4-phenyl-2-mercaptoimidazole 4-phenyl-5-methyl-2-mercaptothiazole4-phenyl-S-methyI-Z-mercaptooxazole4-phenyl-5-methyl-2-mercaptoimidazole Z-mercaptobenzothiazole4-phenyl-2-mercaptobenzothiazole 6-phenyI-Z-mercaptobenzothiazole2-mercapto-tetrahydrobenzothiazole 2-mercapto-naphthothiazoleZ-mercapto-benzooxazole A preferred class of such activators is the2-mercaptothiazoles and related compounds convertible thereinto,including the Z-mercaptothiazoles and the Z-mercaptobenzothiazoles.Other activators include Z-mercapto- 4,5,6,7-tetrahydrobenzothiazole,Z-mercaptothiazoline, 2- mercaptoimidazole, 2 mercaptobenzimidazole, 2mercaptooxazole, and Z-mercaptoimidazoline. In addition, certainaldehyde reaction products of the azole mercaptan accelerators are knownto decompose to the mercaptan and free aldehyde at conventional rubbercuring temperatures, such as at about 250 F. to about 350 F. An exampleof such accelerator is the formaldehyde reaction product ofZ-mer-captobenzothiazole.

The non-flammable polyurethane reaction mixture solutions of thisinvention are particularly useful for applying protective polyurethanelinings to storage tanks and particularly metal storage tanks. Generallythe interior surface of a metallic tank such as a tank made of iron,steel, aluminum, or an alloy of these metals is cleaned with a suitablesolvent such as an aliphatic or aromatic hydrocarbon or with aninorganic acid or base, by steam, by shot or sand-blasting, or acombination of these methods before the polyurethane reaction mixturesolution is applied. If desired, a bonding cement can be applied to thecleaned surface and allowed to dry until tack-free, prior to applicationof the polyurethane reaction mixture in order to enhance the bonding ofthe polyurethane coating to the tank.

Also, if desired, :a caulking compound can be applied to various seams,cracks, and sharp edges on the interior of the tank prior to applicationof the polyurethane reaction mixture. Any suitable caulking compound maybe used. An example of a suitable caulking compound is a polyurethanepolymer. Such a polyurethane polymer can be prepared by mixing aprepolymer with a crosslinking agent. The prepolymer can be prepared byreacting six moles of toluene diisocyanate (a mixture of 2,4 toluenediisocyanate and 2,6 toluene diisocyanate in an 80/20 mole ratio) with amixture of polyesters comprising about one mole of tetramethyleneadipate having a molecular weight of from about 1000 to about 2500 andabout two moles of an 80 ethylene-20 propylene adipate having amolecular weight of from about 1000 to about 2500. Two hundred parts byweight of prepolymer are mixed with 50 parts by weight of methyl ethylketone and 14 parts by weight of CAB-O-SIL and then added to across-linking solution which is prepared by mixing 15.4 parts by weightof 4,4'-methylene bischloroaniline with 15.4 parts by weight of methylethyl ketone. The polyurethane caulking compound is applied to theseams, cracks, and sharp edges of the interior of the tank and cured.

The polyurethane coating is then generally applied to the interiorsurface of the tank in a thickness of from about 5 to about 100 mils.The thickness of the coating is determined by regulating the number ofcoats of solution applied. Generally, each coat is at least partiallycured before a subsequent coat is applied.

It is desirable for the polyurethane reaction mixture to have properthixotropic characteristics as this facilitates even application of thereaction mixture. The solution should have sufficient thixotropiccharacteristics so that it does not flow excessively or form droplets orstreaks on vertical or overhead walls after it is applied to an interiorsurface and before the polyurethane reaction mixture is cured. Variousmethods can be employed to enhance the thixotropic character of thepolyurethane reaction mixture. For example, a submicroscopic pyrogenicsilica may be added to and mixed with the prepolymer solution or thereaction mixture. The type silica prepared in a hot gaseous environmentby the vapor phase hydrolysis of silicon tetrachloride available underthe trademark CAB-O-SIL from Godfrey L. Cabot, Inc., has been found tobe satisfactory. When the prepolymer solution is heated to a temperaturein the range of from about 30 C. to about 100 C. and preferably about 80C. to about 90 C. prior to mixing the silica with the prepolymersolution, less of the silica is required. Leveling agents such ascellulose acetate butyrate and similar materials can be used.Thixotropic characteristics can also be imparted to the mixture throughregulating the curing rate of the reaction mixture, by utilizing properdiamines, and/or by adding a catalytic material to the mixture asheretofore discussed and illustrated.

If desired, pigments, surface active agents and other compounding agentscan be added to the prepolymer solutions. Pigments can be used inamounts of from 0.5 to 50 parts by weight based on 100 parts of theprepolymer used. Generally when pigments are used they are used in theamount of from 1 to 2 parts by weight based on 100 parts of theprepolymer used.

The following procedures further illustrate the invention. In theseprocedures the parts referred to are by weight unless otherwiseindicated.

Procedure A One hundred parts of polypropylene ether glycol having anaverage molecular weight of about 1000 were mixed with 34.8 parts oftoluene diisocyanate (a mixture of 2,4- toluene diisocyanate and2,6-toluene diisocyanate in an /20 mole ratio) at about 70 C. Themixture was allowed to react for 50 minutes. The prepolymer formed wasdegassed for 20 minutes. 500 parts of the polyproylene etherglycol-toluene diisocyanate prepolymer prepared were dissolved in 250parts of trichloroethylene. Five parts of Modoflow, a leveling agentavailable from the Monsanto Company, were added and mixed with thesolution.

234 parts of a curative solution were prepared by dissolving 28.8 partsof 4,4-methylene bis-2-chloroaniline in a mixed solvent containing 25.0parts of methylethyl ketone and 40.0 parts of dichloromethane. Theprepolymer solution and the curative solution were then mixed to form apolyurethane reaction mixture solution.

The flammability test was applied to the mixture of the prepolymer andcurative solutions. No flashing or combustion occurred indicating themixture to be non-flammable.

A casting of the polyurethane reaction mixture of approximately 20 milsthickness which was prepared by flowing the mixture onto a glass plateand allowing it to cure at about 24 C., had a tensile strength of about3200 p.s.i. at 290% elongation.

Procedure B A prepolymer was recipe:

parts of polytetramethylene glycol ether having a molecular weight ofabout 1340 were mixed with 26.2 parts of toluene diisocyanate (a 80/20mole ratio of 2,4 and 2,6 toluene diisocyanate) at about 70 C. andallowed to react for about 50 minutes.

A prepolymer solution was then prepared by dissolving 50 parts of theprepolymer in 25 parts of tetrachloroethylene.

20.6 parts of the curative solution prepared as described in Procedure Awere added to the prepolymer solution. The mixture was tested forflammability and classed as non-flammable.

The mixture was then cured at about 24 C. to form a rubbery polyurethanesheet of about 20 mils thickness having a tensile strength of about 6000p.s.i. at 450% elongation.

The following representative examples further illustrate this invention.The parts and percentages referred to are by weight unless otherwiseindicated.

EXAMPLE I A prepolymer was prepared by reacting six moles of toluenediisocyanate (a mixture of 2,4 toluene diisocyanate and 2,6 toluenediisocyanate in an 80/20 mole ratio) with a mixture of polyesterscomprising one mole of tetrarnethylene adipate having a molecular weightof about 1800 and two moles of an 80 ethylene-20 propylene adipatehaving a molecular weight of about 1800. 300 parts of the prepolymerwere dissolved in parts of trichloroethylene. Then 9.4 parts ofCAB-O-SIL were added to the solution and mixed in with stirring,following prepared according to the following which parts of a 10%cellulose acetate-butyrate in Cellosolve acetate as a leveling agentwere added and mixed with the prepolymer mixture.

A curative solution was prepared by dissolving 28.8 parts of4,4-methylene bis-chloroaniline in a solvent mixture of 25.0 parts ofmethyl ethyl ketone and 40.0 parts of dichloromethane.

The prepolymer solution was mixed with the curative solution in a ratioof 5.2 to 1 of prepolymer solution to curative solution by weight atabout 70 F. The resulting mixture had a pot life of one hour and had setup or cured to the extent that it could not be applied to a surface byconventional spraying techniques after this period of time.

The mixture of the prepolymer and curative solution was tested forflammability and classed as non-flammable. The solution thus preparedwas used to coat the interior surface of a tank truck according to thefollowing procedure.

A three-compartment aluminum tank truck trailer of 8000 gallon capacitywas cleaned by sand-blasting and any loose grit was removed by vacuumsweeping. A bonding cement was sprayed onto the cleaned interior surfaceof the tank and dried to enhance the adhesion of the polyurethane to thesurface. A spray coat of the polyurethane reaction mixture solution wasthen applied to the interior of the tank, and allowed to cure 24 hoursat about 24 C. A second coat was then applied and also allowed to cureat about 24 C. for 24 hours to form a protective rubbery polyurethaneliner.

While certain representative embodiments and details have been shown forthe purpose of illustrating this invention it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

1. A method of forming a protective seamless innerliner on the interiorsurface of a metal storage container which comprises applying at leastone spray coat of a non-flammable liquid polyurethane reaction mixtureto the interior surface of the said container and curing the spray coatsof polyurethane mixture to form the innerliner, Where the liquidpolyurethane reaction mixture is prepared by:

(a) reacting at least one organic diisocyanate with at least onereactive hydrogen containing compound at a temperature of from about C.to about 150 C. where the mole ratio of isocyanato groups to hydroxylgroups of the reactive hydrogen containing compound is from about 1.2/1to about 2.5/1 to form a prepolymer where thereactive-hydrogen-containing compound is selected from the groupconsisting of:

(1) polyhydroxyl polymers having a molecular weight of from about 750 toabout 3500 selected from polytetramethylene ether glycols, castor oil,hydroxyl terminated linear polymeric polyesters derived from a glycoland an organic dicarboxylic acid, and

(2) polyhydroxyl polymers having an average molecular weight of fromabout 1000 to about 3500 and a corresponding hydroxyl number of fromabout 112 to about 28, respectively, selected from polyhydroxyl 1,4addition polymers of isoprene and 1,4 addition polymers of 1,3-butadiene;

(b) dissolving the said prepolymer in a solvent selected from at leastone of the group consisting of dichloroethylene, trichloroethylene,1,1,2,2 tetrachloroethylene, methyl chloroform, dichloromethane, 1,2-dichloroethane, trichloroethane, and 1,1,2,2-tetrachloroethane to form aprepolymer solution; and

(c) mixing an aromatic diamine with the prepolymer solution in a ratioof from about 0.5/1 to about 1.5/1 moles of amino groups per mole ofeach isocyanato group in excess of the moles of hydroxyl groups of thesaid reactive hydrogen-containing polymeric material to form thenonflammable liquid polyurethane reaction mixture.

2. A method according to claim 1 where the said nonfiammable mixture ischaracterized by not supporting combustion when 20 to 25 cubiccentimeters of the said mixture at to F. are placed in a 40 to 50 cubiccentimeter container having a diameter of from 2 to 2 /2 inches andexposed for 5 seconds to a flame having a temperature of from 700 C. to800 C. located one-half inch from the surface of the said mixture.

3. A method according to claim 1 wherein the polyhydroxyl polymers areselected from polyhydroxyl 1,4- addition polymers of isoprene and 1,4addition polymers of 1,3 butadiene having an average molecular weight offrom about 1000 to about 3500 and a corresponding hydroxyl number offrom about 112 to about 28, respectively.

4. A method according to claim 1 where an accelerator having the generalformula HSA is mixed with the nonflammable polyurethane reaction mixturewhere A is selected from the group consisting of thiazole, oxazole,imidazole and imidazoline radicals.

5. A method according to claim 4 wherein the accelerator is2-mercaptobenzothiazole.

6. A method according to claim 1 Where sub-microscopic pyrogenic silicais mixed with the non-flammable prepolymer solution.

References Cited UNITED STATES PATENTS 2,929,800 3/1960 Hill. 2,962,47011/ 1960 Jung. 3,03 6,878 5/1962 Polansky.

JULIUS FROME, Primary Examiner.

